Generation of high strength metal through formation of nanocrystalline structure by laser peening

ABSTRACT

A method of processing a metal piece comprises a number of steps. One step comprises directing a laser beam onto the metal piece for laser peening the metal piece. Another step comprises causing relative movement between the laser beam and the metal piece. Another step comprises providing a tamping material between the laser beam and the metal piece. Another step comprises continuing the laser peening to induce rapid strain and substantial strain in the metal piece and inducing the formation of nanocrystalline structure in the metal piece.

The United States Government has rights in this invention pursuant toContract No. W-7405-ENG-48 between the United States Department ofEnergy and the University of California for the operation of LawrenceLivermore National Laboratory.

BACKGROUND

1. Field of Endeavor

The present invention relates to the generation of high strength metaland more particularly to the generation of high strength metal by laserpeening.

2. State of Technology

U.S. Pat. No. 6,258,185 for methods of forming steel issued Jul. 10,2001 to Daniel J. Branagan and Joseph V. Burch provides the followingstate of technology information: “Steel is a metallic alloy which canhave exceptional strength characteristics, and which, accordingly, iscommonly utilized in structures where strength is required oradvantageous. Steel can be utilized in, for example, the skeletalsupports of building structures, tools, engine components, andprotective shielding of modern armaments. The composition of steelvaries depending on the application of the alloy. For purposes ofinterpreting this disclosure and the claims that follow, “steel” isdefined as any iron-based alloy in which no other single element(besides iron) is present in excess of 30 weight percent, and for whichthe iron content amounts to, at least, 55 weight percent, and carbon islimited to a maximum of 2 weight percent. In addition to iron, steelalloys can incorporate, for example, manganese, nickel, chromium,molybdenum, and/or vanadium. Steel alloys can also incorporate carbon,silicon, phosphorus and/or sulfur. However, phosphorus, carbon, sulfurand silicon can be detrimental to overall steel quality if present inquantities greater than a few percent. Accordingly, steel typicallycontains small amounts of phosphorus, carbon, sulfur and silicon. Steelcomprises regular arrangements of atoms, with the periodic stackingarrangements forming 3-dimensional lattices which define the internalstructure of the steel. The internal structure (sometimes called“microstructure”) of conventional steel alloys is always metallic andpolycrystalline (consisting of many crystalline grains). Steel istypically formed by cooling a molten alloy. The rate of cooling willdetermine whether the alloy cools to form an internal structure thatpredominately comprises crystalline grains, or, in rare cases, astructure which is predominately amorphous (a so-called metallic glass).Generally, it is found that if the cooling proceeds slowly (i.e., at arate less than about 10⁴ K/s), large grain sizes occur, while if thecooling proceeds rapidly (i.e., at a rate greater than or equal to about10⁴ K/s) microcrystalline internal grain structures are formed, or, inspecific rare cases amorphous metallic glasses are formed. Theparticular composition of the molten alloy generally determines whetherthe alloy solidifies to form microcrystalline grain structures or anamorphous glass when the alloy is cooled rapidly. Also, it is noted thatparticular alloy compositions have recently been discovered which canlead to microscopic grain formation, or metallic glass formation, atrelatively low cooling rates (cooling rates on the order of 10 K/s), butsuch alloy compositions are, to date, bulk metallic glasses that are notsteels. Both microcrystalline grain internal structures and metallicglass internal structures can have properties which are desirable inparticular applications for steel. In some applications, the amorphouscharacter of metallic glass can provide desired properties. Forinstance, some glasses can have exceptionally high strength andhardness. In other applications, the particular properties ofmicrocrystalline grain structures are preferred. Frequently, if theproperties of a grain structure are preferred, such properties will beimproved by decreasing the grain size. For instance, desired propertiesof microcrystalline grains (i.e, grains having a size on the order of10⁻⁶ meters) can frequently be improved by reducing the grain size tothat of nanocrystalline grains (i.e., grains having a size on the orderof 10⁻⁹ meters). It is generally more problematic to form grains ofnanocrystalline grain size than it is to form grains of microcrystallinegrain size. Accordingly, it is desirable to develop improved methods forforming nanocrystalline grain size steel materials. Further, as it isfrequently desired to have metallic glass structures, it is desirable todevelop methods of forming metallic glasses.”

United States Patent application No. 2003/0183306 for Selectedprocessing for non-equilibrium light alloys and products by FranzHehmann and Michael Weidemann, published Oct. 2, 2003, provides thefollowing state of technology information: “Aerospace applicationsrequire metallic materials with self-healing surface films to protectthe interior, i.e., the bulk material when exposed to air (includingrain independent on environmental particulars). None of the existingmagnesium engineering alloys exhibit a surface passivation upon exposureto normal atmospheres containing saline species as it is known fortitanium and aluminum alloys. For iron it is the allotropy which allowsfor passivation by equilibrium alloying austenitic and ferritic ironwith chromium, for example. The absence of allotropy for aluminum, forexample, results in deterioration of corrosion behavior of aluminum uponequilibrium alloying and this applies more seriously to magnesiumalloys. Magnesium alloys yet represent the worst case among structuralmetals for aeronautical applications, since magnesium has not only noallotropy as titanium and iron, but Magnesium does also not develop apassive surface film on exposure to normal atmospheres as is evident forpure titanium and pure aluminum. None of the existing conventionalmagnesium alloys have yet shown pronounced passivation behavior byalloying as—by definition—becomes evident upon a significant decrease incorrosion rates compared to the pure metal. Hehmann et al. have shown 5however, that significant passivation is possible by alloying the αMgsolid solution with at least 17 wt. % Al in the supersaturated state.This type of passivation, however, was not obtainable unless veryextreme conditions of rapid solidification from the melt were appliedand it was therefore restricted to thin cross-sections and notobtainable by conventional ingot metallurgy. An engineering solution tothis problem would provide the driving force to resolve many of theobstacles for the introduction of advanced light alloys, but thesolution to this problem has not been recognized as a combined problemof the development of non-equilibrium new and/or established lightalloys as well as of corresponding processes.”

SUMMARY

Features and advantages of the present invention will become apparentfrom the following description. Applicants are providing thisdescription, which includes drawings and examples of specificembodiments, to give a broad representation of the invention. Variouschanges and modifications within the spirit and scope of the inventionwill become apparent to those skilled in the art from this descriptionand by practice of the invention. The scope of the invention is notintended to be limited to the particular forms disclosed and theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

The present invention provides a method of processing a metal piece. Themethod comprises a number of steps. One step comprises directing a laserbeam onto the metal piece for laser peening the metal piece. Anotherstep comprises causing relative movement between the laser beam and themetal piece. Another step comprises providing a tamping material betweenthe laser beam and the metal piece. Another step comprises continuingthe laser peening to induce rapid strain and substantial strain in themetal piece and inducing the formation of nanocrystalline structure inthe metal piece.

The present invention has many uses, including the following uses.Industrial production of ultra-high strength nano-ferrite nano-carbidesteels and other alloys. Processing of high carbon steel components toachieve desired ultra-high strength in specific areas. Production ofultra-high strength steels and other alloys for weapons applications.Industrial production of ultra-high strength nano-ferrite nano-carbideFe—C steel alloys. Industrial production of ultra-high strength alloys.Processing of high carbon steel components to achieve desired ultra-highstrength in specific areas. Production of steels possessing highstrain-rate superplasticity (HSRS) at high temperature. Production ofsteels possessing low temperature superplasticity.

The invention is susceptible to modifications and alternative forms.Specific embodiments are shown by way of example. It is to be understoodthat the invention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of the specification, illustrate specific embodiments of theinvention and, together with the general description of the inventiongiven above, and the detailed description of the specific embodiments,serve to explain the principles of the invention.

FIG. 1 illustrates one embodiment of a system the generation of highstrength metal through the formation of nanocrystalline structure bylaser peening.

FIG. 2 illustrates one embodiment of a method for the generation of highstrength metal through the formation of nanocrystalline structure bylaser peening.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the following detailed description, the drawingfigures, and to incorporated materials, detailed information about theinvention is provided including the description of specific embodiments.The detailed description serves to explain the principles of theinvention. The invention is susceptible to modifications and alternativeforms. The invention is not limited to the particular forms disclosed.The invention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

Referring to FIG. 1, one embodiment of a system is illustrated for thegeneration of high strength metal through the formation ofnanocrystalline structure by laser peening. The system is designatedgenerally by the reference numeral 10. The system 10 uses laser peeningin creating high strength steel and other alloys through the creation ofnanocrystalline structure (NS). Favorable conditions to create NSinclude a large strain and a high strain rate.

In the system 10, a laser 11 and optical system 12 direct a laser beam18 onto a metal work piece 15. The metal piece 15 can be in the form ofplate, sheet, or other configurations. The work piece 15 can be heldstationary and the laser beam 18 moved or the work piece 15 can be movedby a part manipulator 14 with the laser beam 18 stationary. A source offluid 13 directs a fluid stream 19 onto the work piece 15.

The system 10 uses laser peening with one or multiple layers of peeningapplied to the metal piece 15 so as to induce rapid strain andsubstantial strain to induce the formation of nanocrystalline structure.Formation of nanocrystalline structure (grain size smaller than 100 nm)in eutectoid steel and other metal alloys by severe plastic deformationhas been of keen interest over the past decade. Various severe plasticdeformation (SPD) methods including ball drop, ball milling, highpressure torsion, ultrasonic shot peening and air blast shot peeninghave been employed to produce nanocrystalline materials. Nanostructuringhas been used to improve the mechanical properties of bulk metals andalloys. According to the current theories of strengthening of Fe—Csteels refinement of ferrite grain size and of the carbide particle sizepromotes essential rise of strengthening. Moreover, microcrystallinematerials can demonstrate high strain-rate superplasticity (HSRS) stateat high temperature. Super high mechanical properties could be expectedwhen extrapolating this tendency to nanocrystalline structures.Traditional deformation methods (elongation, compression, ruling, draft,etc.) are effective only on thin samples (e.g., wires).

Nanocrystalline solids, in which the grain size is in the nanometerrange, often have technologically interesting properties such asincreased hardness. Nanocrystalline metals can now be produced inseveral ways resulting in a polycrystalline metal with the grainsrandomly oriented. The hardness and yield strength of the materialtypically increase with decreasing grain size according to the relationknown as the Hall-Petch effect. At the smallest grain sizes the oppositeeffect is sometimes reported. This is explained as follows. Most of theplastic deformation occurs in the grain boundaries in the form of alarge number of small “sliding” events, in which only a few atoms (orsometimes a few tens of atoms) move with respect to each other.Occasionally a partial dislocation is nucleated at a grain boundary andmoves through a grain. Such events are responsible for a minor part ofthe total deformation, but in the absence of diffusion they are requiredto allow for deformations of the grains as they slide past each other.As the grain size is reduced, a larger fraction of the atoms belongs tothe grain boundaries, and grain boundary sliding becomes easier. Thisleads to a softening of the material as the grain size is reduced. Thisso-called reverse Hall-Petch effect has been observed experimentally.

The laser 11 and optical system 12 can be various laser systems. Aspecific laser system that can be used for the laser 11 and optic system12 can be a Nd:glass laser with outputs approximately 20 J per pulse at18 to 25 ns pulse duration directed onto the surface of the metal piece15 at an irradiance of 200 J/cm2 and a power density of 10 GW/cm2. Theseparameters can be varied according to the reaction of the particularwork piece 15 being treated. The surface of the work piece 15 can becovered with an ablation/absorption layer such as PVC tape, aluminumtape or paint. Multiple layers of peening can be applied until the workpiece achieves the desired nanocrystalline structure and strength.

The laser 11 and optic system 12, with its nanosecond pulse duration andcontrollable high peak pressure, creates these favorable conditionsbetter than methods such as ball milling, high pressure torsion andultrasonic or air blast shot peening. Because the laser 11 can processlarge areas of arbitrary surface geometry, this process can be used inan industrial processing format for flat plate material as well as inlarge geometry and complicated shaped components.

In the system 10, a source of fluid 13 can be a water nozzle with alaminar stream of water 19 that is applied at the metal surface of thework piece 15 at the point of the laser beam incidence 17. This water 16acts as a tamping medium, increasing the effective pressure and thus theintensity of the developed shock wave. The laser beam 18 and water flowcan be moved systematically over the work piece 15 being processed orthe beam 18 can be held stationary and the metal work piece 15 moved.Combinations of these two can also be used to cover the entire area tobe treated. Multiple layers of peening may require stripping andre-application of the absorption/ablation layer. In peening multiplelayers, the spot positions of the individual beams are offset insuccessive applications. Entire bulk material can be treated in themanner or the laser can be applied to selected parts of metal componentsadding the strength where desired.

The near field output of the beam 18 from laser 11 is image relayed tothe work piece 15 to be peened. In one embodiment, the front surface ofthe work piece 15 is coated with an ablative layer and a pressureconfinement (tamping) layer of fluid 19 is flowed over the ablativelayer. This layer, transparent to the laser light, confines the plasmapressure that develops and greatly increases the intensity of the shockwave that transmits into the metal.

In the process, laser light of typically 100 to 200 J/cm2 passes througha confining layer (typically 1 mm thickness of water) and is incident onan ablation layer (typically a plastic of a few hundred micronthickness) to create a high pressure shock wave. Although the laserpulse lasts for only 20 ns, the shock wave propagates through the bladeat acoustic sound speed which is approximately 4000 meters per secondfor titanium 6-4 alloy. In order to travel a thickness of 1 mm to 2 mmrequires 250 ns to 500 ns.

The system 10 can use a number of laser systems. For example the systemcan use laser systems such as the laser systems illustrated in U.S. Pat.Nos. 5,689,363 and 6,198,069, the disclosures of which are incorporatedherein by reference. One embodiment of the system 10 utilizes a laser 11and optic system 12 such as that shown in U.S. Pat. No. 5,689,363. Thisembodiment of the system 10 utilizes a long-pulse-width,narrow-bandwidth, solid state laser system. The laser system includes anoscillator/preamplifier comprising, e.g., a single frequency Nd:YLFlaser oscillator or preamplifier. An oscillator/preamplifler produces asingle frequency laser beam. The beam has a wavelength of 1054 nm, at240 ns FWHM and typically 60 mJ of power. Upon exiting theoscillator/preamplifier, the beam is polarized horizontally. The beammaintains this polarization as it reflects from turning mirrors, passesthrough a Faraday isolator and negative lens, reflects from mirror,passes through a positive collimating lens, reflects from mirror and ismasked by an input mask. A polarizing beamsplitter is oriented totransmit P-polarization, and thus, transmits a horizontally polarizedbeam. The beam conditioning optics include an anamorphic relay telescopeand collimating lens which prepare the beam size to fit the requiredaperture of the amplifier. The beam reflects from mirrors and transmitsthrough polarizing beamsplitter which is configured to transmitP-polarization and reflect S-polarization. The transmitter beam isrelayed by 1:1 relay telescope to a two-pass optical axis using mirrors.The amplifier is place on axis with this two-pass optical axis. Afterpassing through relay telescope again, the polarization of the beam isrotated 90.degree. by a quartz rotator to the vertical plane. The beamis then reflected by polarizing beamsplitter to be re-injected into theamplification system by polarizing beamsplitter.

After two more amplification passes, the polarization of beam is againrotated 90.degree allowing transmission through the beamsplitter,reflection from mirror and entrance into a Four-wave mixing SBS phaseconjugator, which reverses the phase of beam. Upon reversal ofdirection, the horizontally polarized beam undergoes 4 moreamplification passes and propagating through the polarizingbeamsplitter, collimating lens, anamorphic relay telescope, conditioningoptics, and Faraday isolator, the beam exits the system at thepolarizing beamsplitter, which is configured to reflect S-polarization.A mirror directs the beam through a second harmonic generator. If thepreamplifier produces a pulse at 60 mJ, 240 ns FWHM and 105.4 .mu.m, theoutput from second harmonic generator will be a pulse of about 16 J, atgreater than 500 ns and 527 nm wavelength.

The 45 degree Faraday and quartz rotator set result in a totallypassively switched beam train. The beam enters the amplifier system fromthe oscillator through the anamorphic telescope which takes it from asquare 25.times.25 mm size to the 8.times.120 mm required by the glassamplifier aperture. In this design, the output passes back through thesame telescope, restoring the 25.times.25 mm square beam shape. Theinput beam enters the regenerative amplifier ring in p-polarizationthrough a polarizing beamsplitter, and undergoes two gain passes. Thepolarization is then rotated 90 degrees by the quartz rotator and it nowreflects from the same beamsplitter in s-polarization and undergoes twomore gain passes. When the polarization is returned to the originalp-state after the second pass through the rotator the beam is coupledout through a polarizing beamsplitter in the ring and directed into theSBS four-wave mixing conjugator. The reflected beam from the conjugatorretraces the path of the input beam, resulting in four more gain passesfor a total of eight. The polarization rotation of the 45 degree Faradayrotator and the 45 degree quartz rotator canceled each other in theinput direction but now, in the output direction, they add resulting ina full 90 degree rotation, and the amplified beam is reflected off thefirst polarizing beamsplitter and enters the doubler.

Referring to FIG. 2, another embodiment of a system for the generationof high strength metal through the formation of nanocrystallinestructure by laser peening is illustrated. FIG. 2 is a flow chartillustrating a method of processing a metal piece. The method isdesignated generally by the reference numeral 20. The method 20 useslaser peening in creating high strength steel and other alloys throughthe creation of nanocrystalline structure (NS). Favorable conditions tocreate NS include a large strain and a high strain rate.

The method of processing a metal piece 20 comprises a number of steps.The first step 21 comprises directing a laser beam onto the metal piecefor laser peening the metal piece. The next step 22 comprises causingrelative movement between the laser beam and the metal piece. The nextstep 23 comprises providing a tamping material between the laser beamand the metal piece. The next steps 24 and 25 comprise continuing thelaser peening to induce rapid strain and substantial strain in the metalpiece and inducing the formation of anocrystalline structure in themetal piece.

Formation of nanocrystalline structure (grain size smaller than 100 nm)in eutectoid steel and other metal alloys by severe plastic deformationhas been of keen interest over the past decade. Various severe plasticdeformation (SPD) methods including ball drop, ball milling, highpressure torsion, ultrasonic shot peening and air blast shot peeninghave been employed to produce nanocrystalline materials. Nanostructuringhas been used to improve the mechanical properties of bulk metals andalloys. According to the current theories of strengthening of Fe-Csteels refinement of ferrite grain size and of the carbide particle sizepromotes essential rise of strengthening. Moreover, microcrystallinematerials can demonstrate high strain-rate superplasticity (HSRS) stateat high temperature. Super high mechanical properties could be expectedwhen extrapolating this tendency to nanocrystalline structures.Traditional deformation methods (elongation, compression, ruling, draft,etc.) are effective only on thin samples (e.g., wires).

Nanocrystalline solids, in which the grain size is in the nanometerrange, often have technologically interesting properties such asincreased hardness. Nanocrystalline metals can now be produced inseveral ways resulting in a polycrystalline metal with the grainsrandomly oriented. The hardness and yield strength of the materialtypically increase with decreasing grain size according to the relationknown as the Hall-Petch effect. At the smallest grain sizes the oppositeeffect is sometimes reported. This is explained as follows. Most of theplastic deformation occurs in the grain boundaries in the form of alarge number of small “sliding” events, in which only a few atoms (orsometimes a few tens of atoms) move with respect to each other.Occasionally a partial dislocation is nucleated at a grain boundary andmoves through a grain. Such events are responsible for a minor part ofthe total deformation, but in the absence of diffusion they are requiredto allow for deformations of the grains as they slide past each other.As the grain size is reduced, a larger fraction of the atoms belongs tothe grain boundaries, and grain boundary sliding becomes easier. Thisleads to a softening of the material as the grain size is reduced. Thisso-called reverse Hall-Petch effect has been observed experimentally.

In the method 20, laser light of typically 100 to 200 J/cm2 passesthrough a confining layer (typically 1 mm thickness of water) and isincident on an ablation layer (typically a plastic of a few hundredmicron thickness) to create a high pressure shock wave. Although thelaser pulse lasts for only 20 ns, the shock wave propagates through theblade at acoustic sound speed which is approximately 4000 meters persecond for titanium 6-4 alloy. In order to travel a thickness of 1 mm to2 mm requires 250 ns to 500 ns.

In the method of processing a metal piece 20 the laser peening can beaccomplished with a laser producing nanosecond pulse duration andcontrollable high peak pressure sufficient to induce rapid strain andsubstantial strain in the metal piece and induce the formation ofnanocrystalline structure. The laser beam has nanosecond pulse durationand controllable high peak pressure sufficient to induce rapid strainand substantial strain in the metal piece and induce the formation ofnanocrystalline structure. In one embodiment of the method 20 the laserbeam provides an output of approximately 20 J per pulse at 18 to 25 nspulse duration directed onto the surface of the metal piece at anirradiance of approximately 200 J/cm2 and a power density ofapproximately 10 GW/cm2. The method 20 can include applying multiplelayers of laser peening to the metal piece. In one embodiment of themethod of processing metal 20, the laser beam is directed onto the metalpiece at a point of the laser beam incidence and a tamping material isprovided between the laser beam and the metal piece. This may beaccomplished by applying a laminar stream of water to the metal piece atthe point of the laser beam incidence.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A method of processing a metal piece, comprising the steps of:directing a laser beam onto the metal piece for laser peening the metalpiece, causing relative movement between said laser beam and the metalpiece, providing between said laser beam and the metal piece a tampingmaterial that is essentially transparent to the laser beam, andcontinuing said laser peening to induce rapid strain and substantialstrain in the metal piece and inducing the formation of nanocrystallinestructure in the metal piece.
 2. The method of processing a metal pieceof claim 1 wherein said laser peening is accomplished with said laserproducing nanosecond pulse duration and controllable high peak pressuresufficient to induce rapid strain and substantial strain in the metalpiece and induce the formation of nanocrystalline structure.
 3. Themethod of processing a metal piece of claim 1 wherein said laser beamhas pulse duration in the range of several hundred picoseconds to 10 sof nanoseconds and controllable high peak pressure sufficient to inducerapid strain and substantial strain in the metal piece and induce theformation of nanocrystalline structure.
 4. The method of processing ametal piece of claim 1 wherein said laser beam provides an output ofapproximately 20 J per pulse at 18 to 25 ns pulse duration directed ontothe surface of the metal piece at an irradiance of approximately 200J/cm2 and a power density of approximately 10 GW/cm2.
 5. The method ofprocessing metal of claim 1 wherein said step of continuing said laserpeening comprises applying multiple layers of laser peening to the metalpiece.
 6. The method of processing metal of claim 1 wherein said step ofcausing relative movement between said laser beam and the metal piececomprises moving said laser beam over the metal piece.
 7. The method ofprocessing metal of claim 1 wherein said step of causing relativemovement between said laser beam and the metal piece comprises movingthe metal piece relative to said laser beam.
 8. The method of processingmetal of claim 1 wherein said steps of directing a laser beam onto themetal piece and continuing said laser peening comprise applying peeningto metal plate.
 9. The method of processing metal of claim 1 whereinsaid steps of directing a laser beam onto the metal piece and continuingsaid laser peening comprise applying peening to metal sheet.
 10. Themethod of processing metal of claim 1 wherein said laser beam isdirected onto the metal piece at a point of the laser beam incidence andsaid step of providing a tamping material between said laser beam andthe metal piece comprises applying a tampering material that exhibit theelectro-strictive effect, are transparent to the laser light, and have alow SBS gain coefficient between said laser beam and the metal piece.11. The method of processing metal of claim 1 wherein said laser beam isdirected onto the metal piece at a point of the laser beam incidence andsaid step of providing a tamping material between said laser beam andthe metal piece comprises applying a laminar stream of water to themetal piece at the point of the laser beam incidence.
 12. The method ofprocessing metal of claim 1 wherein said step of providing an ablationmaterial between said laser beam and the metal piece comprises coveringthe metal piece an ablation/absorption layer.
 13. A method of processinga metal piece, comprising the steps of: directing a laser beam onto themetal piece for laser peening the metal piece, causing relative movementbetween said laser beam and the metal piece, providing anablative/insulating material adhered to or in intimate contact with themetal piece between said laser beam and the metal piece, providing atamping material that is essentially transparent to the laser beam, andcontinuing said laser peening to induce rapid strain and substantialstrain in the metal piece and inducing the formation of nanocrystallinestructure in the metal piece.
 14. The method of processing a metal pieceof claim 13 wherein said laser peening is accomplished with said laserproducing nanosecond pulse duration and controllable high peak pressuresufficient to induce rapid strain and substantial strain in the metalpiece and induce the formation of nanocrystalline structure.
 15. Themethod of processing a metal piece of claim 13 wherein said laser beamhas pulse duration in the range of several hundred picoseconds to 10 sof nanoseconds and controllable high peak pressure sufficient to inducerapid strain and substantial strain in the metal piece and induce theformation of nanocrystalline structure.
 16. The method of processing ametal piece of claim 13 wherein said laser beam provides an output ofapproximately 20 J per pulse at 18 to 25 ns pulse duration directed ontothe surface of the metal piece at an irradiance of approximately 200J/cm2 and a power density of approximately 10 GW/cm2.
 17. The method ofprocessing metal of claim 13 wherein said step of continuing said laserpeening comprises applying multiple layers of laser peening to the metalpiece.
 18. The method of processing metal of claim 13 wherein said stepof causing relative movement between said laser beam and the metal piececomprises moving said laser beam over the metal piece.
 19. The method ofprocessing metal of claim 13 wherein said step of causing relativemovement between said laser beam and the metal piece comprises movingthe metal piece relative to said laser beam.
 20. The method ofprocessing metal of claim 13 wherein said steps of directing a laserbeam onto the metal piece and continuing said laser peening compriseapplying peening to metal plate.
 21. The method of processing metal ofclaim 13 wherein said steps of directing a laser beam onto the metalpiece and continuing said laser peening comprise applying peening tometal sheet.
 22. The method of processing metal of claim 13 wherein saidlaser beam is directed onto the metal piece at a point of the laser beamincidence and said step of providing a tamping material between saidlaser beam and the metal piece comprises applying a laminar stream ofwater to the metal piece at the point of the laser beam incidence. 23.The method of processing metal of claim 13 wherein said step ofproviding an ablation material between said laser beam and the metalpiece comprises covering the metal piece an ablation/absorption layer.24. The method of processing metal of claim 13 wherein said step ofproviding a ablation/insulation material between said laser beam and themetal piece comprises covering at least a portion of the metal piecewith PVC tape.
 25. The method of processing metal of claim 13 whereinsaid step of providing a ablative material between said laser beam andthe metal piece comprises covering at least a portion of the metal piecewith aluminum tape.
 26. The method of processing metal of claim 13wherein said step of providing an ablative material between said laserbeam and the metal piece comprises covering at least a portion of themetal piece with paint.